What type of triangle is defined as having two equal sides?

The correct choice is the Isosceles Triangle, which is defined by having at least two sides that are equal in length. This property gives the isosceles triangle its distinct characteristics, including two equal angles opposite the equal sides. It is a fundamental concept in geometry, as the isosceles triangle can be found in various applications, from architecture to art, due to its symmetrical shape.

In contrast, an Equilateral Triangle has all three sides of equal length, which is a more specific case than the isosceles triangle. A Right Triangle is characterized by having one angle that is exactly 90 degrees, and a Scalene Triangle has all sides of different lengths, meaning it cannot have any equal sides at all. Understanding these distinctions is crucial for recognizing and categorizing triangles in various mathematical contexts.